1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and a method for polishing semiconductor substrates. More particularly, embodiments of the present invention provide apparatus and method for temperature control when polishing semiconductor substrates to improve uniformity.
2. Description of the Related Art
During fabrication of a semiconductor device, various layers, such as oxides, and copper, require planarization to remove steps or undulations prior to formation of subsequent layers. Planarization is typically performed mechanically, chemically, and/or electrically using processes such as chemical mechanical polishing (CMP), and electro-chemical mechanical polishing (ECMP).
Chemical mechanical polishing typically includes mechanically abrading a substrate in a slurry that contains a chemically reactive agent. During chemical mechanical polishing, the slurry is delivered on a polishing pad and the substrate is typically pressed against the polishing pad by a carrier head. The carrier head may also rotate and move the substrate relative to the polishing pad. As a result of the motion between the carrier head and the polishing pads and chemicals included in the slurry, the non-planar substrate surface is planarized by chemical mechanical polishing.
However, various factors of CMP process can lead to non-uniformity causing non-planar artifacts on the substrate surface. For example, during processing, different regions on the substrate may have different speeds relative to the polishing pad and different accessibility to the slurry resulting in temperature variation within different regions of the substrate. Substrate surface temperature is one of the factors that affect removal rate. Consequently, temperature variations within the substrate may lead to non-uniformity, such as non-planar surface, within the substrate.
For example, FIG. 1 illustrates a prior art polishing result with non-uniformity. Plot 10 in FIG. 1 is a profile of a substrate after polishing. The x-axis indicates a distance from a center of the substrate and the y-axis indicates the thickness of the substrate. As shown by the curve 11, there are pumps 12, 13 near the edge of the substrate.
Therefore, there is a need for apparatus and method for improving uniformity in polishing.